All Questions
Tagged with nonparametric wilcoxon-mann-whitney-test
35
questions
140
votes
8
answers
121k
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How to choose between t-test or non-parametric test e.g. Wilcoxon in small samples
Certain hypotheses can be tested using Student's t-test (maybe using Welch's correction for unequal variances in the two-sample case), or by a non-parametric test like the Wilcoxon paired signed rank ...
- 23.8k
24
votes
5
answers
13k
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What exactly does a non-parametric test accomplish & What do you do with the results?
I have a feeling this may have been asked elsewhere, but not really with the type of basic description I need. I know non-parametric relies on the median instead of the mean to compare... something. ...
- 315
16
votes
1
answer
4k
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Why is the Mann–Whitney U test significant when the medians are equal?
I've received a results from a Mann-Whitney rank test that I don't understand.
The median of the 2 populations is identical (6.9). The uppper and lower quantiles of each population are:
6.64 & 7....
- 1,241
15
votes
3
answers
5k
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Why is the asymptotic relative efficiency of the Wilcoxon test $3/\pi$ compared to Student's t-test for normally distributed data?
It is well-known that the asymptotic relative efficiency (ARE) of the Wilcoxon signed rank test is $\frac{3}{\pi} \approx 0.955$ compared to Student's t-test, if the data are drawn from a normally ...
- 23.8k
2
votes
1
answer
2k
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Which statistical analysis should I perform if the data sets are not normally distributed?
I am doing an experiment where there are two independent groups; one is the group of "infected" patients another is the group of "sepsis" patients. I am comparing "platelet monocyte aggregates(PMA)" ...
28
votes
2
answers
19k
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Non-parametric test if two samples are drawn from the same distribution
I would like to test the hypothesis that two samples are drawn from the same population, without making any assumptions about the distributions of the samples or the population. How should I do this?
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- 467
6
votes
2
answers
3k
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How to compare two non-normally distributed samples with very different sizes? (Mann-Whitney vs Randomization/Bootstrap)
Perhaps this is a very basic question, but I didn't find yet a simple solution for this simple problem:
I want to compare two samples (say X and Y) for a continuous variable which is non-normally ...
- 75
6
votes
3
answers
4k
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Mann Whitney Test: Clearing Up Confusion
I have been reading many statistical websites stating that the Mann Whitney test is a test of medians. However, I believe that this is not really true? It is a test of the difference in the ranks. The ...
- 162
6
votes
1
answer
3k
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Difference of 'centers' of 2 non-normal samples with Mann-Whitney test
I have 2 non-normally distributed samples of different sizes (N1~=N2).
To evaluate whether there is a significant difference between these samples, I used the Mann Whitney U test (...
- 1,486
6
votes
2
answers
4k
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How to interpret Mann-Whitney's statistical significance if median is equal?
Testing the difference between the observations of two groups by using Mann-Whitney Test has given the following output (from minitab):
...
1
vote
1
answer
722
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How to find the difference between two set of scores of a single participant?
What I am trying to do?
I have a data set which consists of only one undergraduate student's all courses scores. Let's assume, he has completed about 70 courses where 40 courses are related to ...
- 294
6
votes
2
answers
3k
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Wilcoxon Test - non normality, non equal variances, sample size not the same
I know there are already a lot of posts out there, but I couldn't find this exact combination in any of them.
Comparing two samples (Prices associated with men and with women), but I have neither the ...
- 71
10
votes
1
answer
20k
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How do I interpret the Mann-Whitney U when using R's formula interface
Say we have the following data:
...
- 2,657
6
votes
1
answer
763
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Why are there two forms for the Mann-Whitney U test statistic?
I have encountered two forms for calculating the two-sample Mann-Whitney U test statistic, which are:
$$U_1 = R_1 - \frac{n_1(n_1 + 1)}{2}$$
and
$$U_1 = n_1n_2 + \frac{n_1(n_1+1)}{2} - R_1$$
where ...
- 163
6
votes
2
answers
3k
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How to test group differences when neither parametric nor nonparametric assumptions are met?
Consider following example. We asked 50 men and 50 women one question and they answered on 5 point likert scale (1 is completely disagree and 5 completely agree).
Suppose that 50 men responded 20 ...
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